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At least 397 records · Page 22

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NASA NTRS1985

Dual-Mode Horn Antenna for Millimeter Wavelengths

Millimeter-wave feed horn exhibits nearly equal beam-intensity patterns in E- and H-planes as well as low side-lobe levels. Horn includes circular waveguide step transition, and conical section. Design simplified version of Potter feed-horn design. New feed horn easier to construct, in part because of simpler shape. Reduction in phase change between step transition and aperture increases bandwidth, thereby reducing precision required to manufacture phase-sensitive dimensions of horn.

Pickett, H. M.↗

NASA NTRS1984

A Review of the Millimeter and Centimeter Observations of Uranus

Millimeter and centimeter wave astronomical data of Uranus are presented and discussed. Some recent observations of the brightness distribution across the disk at 2 cm and 6 cm wavelength are reported. Data related to the variability of the microwave spectrum are reanalyzed, taking into account the strong variation of temperature with wavelength, and including up to date data. The results indicate that the brightness temperatures of Uranus have probably reached their maximum values. The evidence for the depletion of ammonia in the upper atmosphere is discussed.

Gulkis, S.↗

NASA NTRS1985

Multifrequency observations of blazars. I - The shape of the 1 micron to 2 millimeter continuum

Near-simultaneous measurements in 11 wavebands between 1 micron and 2 mm of a sample of 13 'blazars' are presented. These measurements represent the first comprehensive attempt to determine the infrared-to-millimeter-wave properties of this class of object, which emit the bulk of their luminosity in the far-infrared region. Most of the sources have very flat millimeter/submillimeter spectra up to the highest observed frequency. However, 3C 279 and 3C 446 show evidence of turnovers in their submillimeter spectra. The 1-4 micron spectra can be characterized by simple power laws, all steeper than -0.9; several sources, however, show evidence of spectral beaks in the 10-20 micron region, suggestive of energy losses. It is shown that the spectral properties are consistent with synchrotron emission from relativistic jets aligned close to the line of sight and the observations are discussed in relation to such models.

Gear, W. K.↗

NASA NTRS1985

Submillimeter, millimeter, and microwave spectral line catalog

This report describes a computer accessible catalogue of submillimeter, millimeter, and microwave spectral lines in the frequency range between 0 and 10000 GHz (i.e., wavelengths longer than 30 micrometers). The catalogue can be used as a planning guide or as an aid in the identification and analysis of observed spectral lines. The information listed for each spectral line includes the frequency and its estimated error, the intensity, lower state energy, and quantum number assignment. The catalogue has been constructed using theoretical least squares fits of published spectral lines to accepted molecular models. The associated predictions and their estimated errors are based upon the resultant fitted parameters and their covariances. Future versions of this catalogue will add more atoms and molecules and update the present listings (151 species) as new data appear. The catalogue is available from the authors as a magnetic tape recorded in card images and as a set of microfiche records.

Poynter, R. L.↗

NASA NTRS1986

Analyzing Millimeter-Wave Mixers

Series of computer programs developed to serve as tool in understanding behavior and subsequent optimization of millimeter-wave mixers. Major program in collection is general mixer-analysis program that performs complete large- and small-signal analysis of mixer with known diode and mount characteristics. Primary objective behind programs to gain better understanding of factors that affect performance of room-temperature, single-ended Schottky-diode mixers operating above 100 GHz.

Siegel, P.↗

NASA NTRS1986

Polar-cap and coronal-hole-associated brightenings of the Sun at millimeter wavelengths

Mapping observations of the Sun at millimeter wavelengths were made on 16 to 22 July 1984 with the 45-m telescope of the Nobeyama Radio Observatory. Seven 36-GHz (8.3-mm) maps and five 98-GHz (3.1-mm) maps were taken with half-power beam widths of 46 arc sec and 17 arc sec, respectively. Instead of the conventional rastering technique, a radial-scan method was adopted in which every scan passes through the disk center. Accordingly, the variation of the atmosphere attenuation due to changes in the weather conditions can be easily estimated and removed by using the brightness values at the disk center as calibration data. Also, the pointing errors of the telescope due to the high-speed scans can be corrected by using the solar limbs as position references. The rms residual errors in relative brightness and position after the corrections were estimated to be approx. 2% and approx. 5 arc sec respectively. To further reduce these errors, enabled us to make high-quality maps with with or approx. 1% uncertainty in brightness. Here and in the following, brightness is expressed in terms of the average brightness of the solar disk as a unit. Note that the brightness temperature of the quiet Sun is approx. 8000 K and approx. 6000 K at 36 GHz and 98 GHz, respectively.

Kosugi, T.↗

NASA NTRS1985

Imaging front-end systems for millimeter waves and submillimeter waves

Imaging (multi-beam) front-end systems utilize a reflector or a lens, as well as a focal-plane array of receptor elements (beams). To be practical, such systems must utilize focal plane arrays which can be fabricated using hybrid integrated (and eventually monolithic) technology. This paper reviews alternative approaches to focussing elements, auxiliary devices required for local oscillator injection and similar functions, and focal plane arrays. It also discusses general limitations and advantages of these approaches, as well as typical applications to millimeter and submillimeter astronomical instrumentation.

Yngvesson, K. S.↗

NASA NTRS1986

A survey of the millimeter-wave spectrum of Sagittarius B2

More than 60 percent of the millimeter wave spectrum between 70 and 150 GHz of the giant Sgr B2 molecular cloud was surveyed with the Bell Laboratories 7 m telescope at a spectral resolution of 1 MHz. The observations and instrumentation are described, including beam efficiency and beamwidth as functions of frequency, frequency coverage, and rms noise. The catalog used to identify the 457 lines found is summarized, and the analysis of the data to determine column densities and rotational temperatures is discussed. The range of rotational temperatures obtained and their relation to the kinetic temperature, and their implications for the hydrogen density, are considered. More than 300 lines are transitions of 21 molecules, and the results for these are analyzed, giving excitation diagrams for most of them. A partly successful attempt is made to use ratios of the calculated abundances to predict abundances of as yet undetected species. Finally, the spectra for the entire survey are presented.

Cummins, S. E.↗

NASA NTRS1985

High resolution millimeter-wave imaging sensor

A scanning 3-mm radiometer is described that has been built for use on a small aircraft to produce real time high resolution images of the ground when atmospheric conditions such as smoke, dust, and clouds make IR and visual sensors unusable. The sensor can be used for a variety of remote sensing applications such as measurements of snow cover and snow water equivalent, precipitation mapping, vegetation type and extent, surface moisture and temperature, and surface thermal inertia. The advantages of millimeter waves for cloud penetration and the ability to observe different physical phenomena make this system an attractive supplement to visible and IR remote sensing systems.

Wilson, W. J.↗

NASA NTRS1986

The laboratory millimeter-wave spectrum of methyl formate in its ground torsional E state

Over 250 rotational transitions of the internal rotor methyl formate (HCOOCH3) in its ground v(t) = 0 degenerate (E) torsional substate have been measured in the millimeter-wave spectral region. These data and a number of E-state lines identified by several other workers have been analyzed using an extension of the classical principal-axis method in the high barrier limit. The resulting rotational constants allow accurate prediction of the v(t) = 0 E substate methyl formate spectrum below 300 GHz between states with angular momentum J not greater than 30 and rotational energy of not more than 350/cm. The calculated transition frequencies for the E state, when combined with the results of the previous analysis of the ground-symmetric, nondegenerate state, account for over 200 of the emission lines observed toward Orion in a recent survey of the 215-265 GHz band.

Plummer, G. M.↗

NASA NTRS1986

The millimeter and submillimeter spectrum of CF(+)

The application of a recently described technique for producing significantly enhanced concentrations of molecular ions for spectroscopic study to the detection and measurement of the millimeter and submillimeter wave spectrum of CF(+) is reported. The experimental procedure is discussed, and the measured absorption frequencies are shown and compared with those calculated from spectral constants. These constants are given together with those from the infrared spectrum by Kawaguchi and Hirota (1985).

Plummer, G. M.↗

NASA NTRS1986

Submillimeter and millimeter observations of solar system objects

The millimeter wavelength 3-element array at OVRO was used to observe Halley's comet in carbon monoxide (negative result) and to set an upper limit from continuum flux of 15 km on the size of the nucleus, assumed to be a black body. The Saturn system was observed with the array and ring brightness temperatures at a wavelength of 2.7 mm were obtained. A B-ring temperature of 30 K was compared to the results at lambda = 2 cm of about 7 K indicates the measurement of true emission from the Ring particles at mm-wavelengths. Brightness temperatures of Titan, Neptune, Uranus, Io, Europa, Ganymede, and Callisto were made, all tied to Mars. Accurate microwave spectra of all these objects from 3 mm to 6 cm were obtained.

Muhleman, D. O.↗

NASA NTRS1986

The proposed NRAO millimeter array and its use for solar studies

A brief summary is given of the proposed National Radio Astronomy Observatory (NRAO) Millimeter Array discussed at a workshop held in Green Bank, W. Va., September 30 to October 2, 1985. A brief description of the solar studies that can be made with such an array is provided.

Kundu, Mukul R.↗

NASA NTRS1987

Research in millimeter wave techniques

The areas of millimeter wave (MMW) research include atmospheric propagation and radiometry, advanced MMW component design with emphasis on quasi-optical techniques, and the development of MMW receivers, especially those using subharmonic mixers. Calculations of atmospheric attenuation and radiometric antenna temperature were made in the range 100 to 700 GHz, together with measurements of atmospheric antenna temperature near 95 and 183 GHz. Quasi-optical components designed include lenses, mirrors, and wire grid devices, as well as feedhorns for interference with waveguide components. Subharmonic mixers with state-of-the-art performance at 183 GHz were also developed. Each of these areas of research is summarized.

Mcmillan, R. W.↗

NASA NTRS1986

Near millimeter wave imaging/multi-beam integrated antennas

Some preliminary results on a mixer design which is suitable for integration with tapered slot antennas have been obtained and published. This mixer design was tested both in a 4 to 10 GHz model, and (slightly modified) at 94 GHz. The latter utilized the same Hewlett-Packard beam-lead diodes which were used as detector diodes in the linearly tapered slot antennas (LTSA) arrays. These diodes are the most rugged to be found, and generally survive well on the flexible Kapton substrates. The 4 to 10 GHz version of this mixer has less than 6 dB conversion loss over an octave bandwidth. It uses a slot ring in a balanced configuration, and requires the LO to be fed through a separate port. A different design for a mixer which may be integrated with an LTSA antenna element is discussed. This mixer was tested at 38 GHz with the same HP beam-lead diodes, and has less than 10 dB conversion loss. Further work on mixers has emphasized theoretical modeling, using a computer program, which takes into account the effect of excess noise of Schottky-barrier diodes for the first time. Calculated results agree quantitatively with measured results on millimeter wave mixers.

Yngvesson, K. Sigfrid↗

NASA NTRS1986

Submillimeter and millimeter observations of Uranus and Neptune

Neptune and Uranus were studied at submillimeter and millimeter wavelengths for 2 yr using the UK IR telescope and the NASA IR telescope at Mauna Kea and the 12 dish at Kitt Peak, AZ. The brightness temperatures of both planets are provided at various wavelengths over the 0.35-3.3 mm interval scanned in the study. The present data, in combination with data from the 17 microns-3 mm interval scanned in the study. The present data, in combination with data from the 17 microns-3 mm interval taken during previous campaigns, are employed to model the temperature structures in the atmospheres of the two planets over the vertical range 100 mbar-8 bar. The data support the presence of active convection processes at the 1 bar level and deeper in both atmospheres. A static equilibrium however, exists between para-H2 and ortho-H2, along with a constant CH4 fraction of 2 percent. Deficiencies in the current database are detailed.

Orton, G. S.↗

NASA NTRS1986

Millimeter-wave imaging sensor

A scanning 3-mm radiometer system has been built and used on a helicopter to produce moderate-resolution (0.5 deg) images of the ground. This millimeter-wave sensor can be used for a variety of remote-sensing applications and produces images through clouds, smoke, and dust when visual and IR sensors are not usable. The system is described and imaging results are presented.

Wilson, W. J.↗

NASA NTRS1986

Millimeter interferometry of the molecular gas in ARP 20

The Owens Valley Millimeter Wave Interferometer has been used to map the 2.6-mm CO emission in the ultraluminous infrared galaxy Arp 220. Approximately 70 percent of the CO emission from the galaxy originates from an unresolved region less than 4 arcsec x 6 arcsec in size (corresponding to 1500 pc diameter) centered on the near-infrared nucleus. The mass of gas within this region is 10 to the 10th solar mass, which is about 30 times greater than that in an equivalent area of the Galaxy. This concentration could result in efficient star formation via cloud-cloud collisions and provide a significant accretion flow onto a compact, central object.

Scoville, N. Z.↗